There are various types of self-attaching female fastener elements, including pierce nuts, which may be formed by cold heading. However, such female fastener elements generally do not form a sealed joint with a metal panel, particularly thin metal panels such as now used by the automotive and appliance industries. Further, pierce nuts formed by cold heading generally do not have sufficient torque resistance for many applications, such as oil pan nuts.
The prior art includes self-attaching female fasteners formed by cold heading including a central annular pilot portion having a bore extending through an annular end face of the pilot portion, an annular flange portion surrounding the pilot portion having a generally planar annular bearing face and an annular groove in the annular bearing face of the flange portion surrounding the pilot portion. During installation of the fastener to a panel, the pilot portion is received through an opening in the panel and a portion of the panel surrounding the opening is deformed into the annular groove. Where the self-attaching female fastener element is a pierce nut, the pilot portion projects above the bearing face of the flange portion and the end face of the pilot portion pierces an opening in the panel. The prior art also includes various anti-rotation means including recesses and protrusions in the bottom or side walls of the groove. However, such anti-rotation means are generally not suitable for thin metal panels and the pierce nuts generally do not form a sealed joint.
There is, therefore, a long felt need for a self-attaching female fastener element, particularly a pierce nut, which may be formed by cold header techniques having sufficient torque resistance particularly with thin metal panels and which forms a sealed joint with the panel for applications requiring a sealed joint including, for example, oil pan nuts and the like. The self-attaching female fastener element, female fastener element and panel assembly and method of forming a sealed joint of this invention achieves these objects in a female fastener element which may be formed by conventional cold header techniques.